Trim only end

if i try and convert a single line that is a code block, the indent at the beginning will get trimmed

so something like

```html
<pre><code>this is a code block</code></pre>
```

gets turned into 

```
this is a code block
```

but i actually want

```
    this is a code block
```

it will work if you have lines before it, just not if you have one line.

tests included.